This invention relates to micromechanical current- or thermally-driven devices and their method of manufacture. In particular, this invention relates to infrared emitters and photonic crystals.
Microelectromechanical systems (MEMS) are very small, often moveable structures made on a substrate using surface or bulk lithographic processing techniques, such as those used to manufacture semiconductor devices. MEMS devices may be moveable actuators, sensors, valves, pistons, or switches, for example, with characteristic dimensions of a few microns to hundreds of microns. A moveable MEMS switch, for example, may be used to connect one or more input terminals to one or more output terminals, all microfabricated on a substrate. The actuation means for the moveable switch may be thermal, piezoelectric, electrostatic, or magnetic, for example.
MEMS may also be non-moving devices, such as photonic devices, fabricated using surface or bulk lithographic processing techniques. In such cases, small features required for the device to emit radiation in a narrow spectrum, for example, may be formed using MEMS techniques. Such a photonic device is a photonic crystal, formed from two metal films separated by a dielectric, with small holes formed in the metal films which determine the radiation output pattern and spectrum of the device. The device may be heated to an operating temperature of about 350 degrees centigrade, by driving a current through the device, and heating it by Joule heating. When the operating temperature is achieved, the photonic device may emit the desired spectrum of radiation, often in the infrared portion of the electromagnetic spectrum.
Since it is desired to heat the photonic device itself, and not the leads delivering the current to the photonic device, ideally, the leads are made from a low resistance material. Furthermore, it is desired that the resistivity of the lead material be stable with time and with heating cycles, such that the operating point and output of the photonic device do not change over time or with repeated use.